This invention relates generally to a multicolor electrophotographic printing machine, and more particularly concerns a device utilized in a developability regulating apparatus used in the printing machine for maintaining a light source and photosensor employed therein substantially free of contaminating deposits.
Toner particle concentration in the developer mix directly effects the developability of the multi-color electrophotographic printing machine. The concentration of toner particles within the developer mix, i.e., the percentage of toner particles relative to carrier granules relates directly to the characteristics of the developed image. For example, the density and contract of the image will be effected by the toner particle concentration.
Numerous systems have been developed which add toner particles to the developer mix. However, most of these systems operate in an open loop fashion, i.e., there is no feedback between the concentration in the mix and the amount of toner particles to be added thereto. Other systems which operate in a closed loop manner are directed primarily to black and white printing machines rather than multi-color printing machines. A typical system used in a black and white printing machine is disclosed in U.S. Pat. No. 3,399,652 issued to Gawron in 1968. This patent discloses a rotating disc disposed in the developer mix. The disc is electrically biased to attract toner particles from the mix. A light beam is reflected from the surface of the disc onto a photoelectric unit. The intensity of the light rays stricking the photoelectric unit is an indication of the toner particle concentration within the developer mix. However, the foregoing system does not have the disc mounted on the photoconductive member, nor is any apparatus associated therewith for maintaining the light source and photoelectric sensor substantially free of toner particle contamination. Hence, it does not undergo the normal processing steps of the photoconductive member and is subjected to toner particle contamination which may introduce erroneous signals.
One system adapted for use in a multi-color electrophotographic printing machine is described in U.S. Pat. No. 3,754,821 issued to Whited in 1973. As disclosed therein, the developability regulating apparatus includes a transparent electrode mounted on the photoconductive member and adapted to attract electrostatically toner particles thereto. A light source develops a beam of light rays which are transmitted from the interior of the photoconductive drum through the transparent electrode onto the photosensor. The photosensor develops an electrical signal indicative of the density of toner particles adhering to the transparent electrode. In the foregoing system, light rays pass through the transparent electrode rather than being reflected therefrom.
In all of the foregoing systems particle contamination introduces added problems thereto. Frequently, particle contamination will produce erroneous signals in the system. For example, when particles are accumulated on the light source, the intensity of the light rays therefrom is diminished and the photosensor will react substantially in the same manner as though toner particles have been deposited on the electrode, i.e., the intensity of the electrical signal will decrease in accordance with the amount of toner particles deposited on the light source. Similarly, if contaminating particles are deposited on the photosensor, the intensity of the signal therefrom will be reduced in proportion to the amount of toner particles deposited thereon. It is, therefore, evident that the accumulation of contaminating particles on both the light source and photosensor of a developability regulating apparatus utilized in an electrophotographic printing machine must be controlled.
Accumulation of particles in a multi-color electrophotographic printing machine is more significant than in a conventional black and white printing machine. A multi-color electrophotographic printing machine utilizes a plurality of toner particles to be capable of reproducing all of the various colors in an original document. This may produce significantly more particle contamination in the printing machine. Thus, the potentiality for contaminating the various components of the developability regulating apparatus is substantially increased.
Accordingly, it is a primary object of the present invention to improve the developability regulating apparatus utilized in a multi-color electrophotographic printing machine by preventing the accumulation of particle contamination thereon.